The present invention relates to an air bag device that maintains safety for the passengers in a vehicle crash, and particularly to an air bag device adapted for use in automobiles.
In order to improve reliability of processing in an air bag control, known prior art controls use two CPUs to perform the same processing, the results are compared by a comparator (that is not guaranteed fail-safe), and an operation signal is output to the air bag device only when the results processed by the two CPUs are the same. Such a control arrangement is described, for example, in SAE Paper 901123 "Sensing and Systems Aspects of Fault Tolerant Electronics Applied to Vehicle Systems."
In Japanese Laid-Open Patent Publication No. 168545/1989, furthermore, a diagnosing circuit (which is likewise not guaranteed for fail-safety) is added to detect any fault that has developed in the air bag device. In this manner, a fault in the system is removed as early as possible, in order to improve reliability. Methods for detecting the occurrence of a failure in computer systems by means of regular self diagnosis are also used in fault tolerant systems, such as railway controls, for example.
One disadvantage of the above-mentioned conventional systems is that two CPU modules (CPUs and memories) are required, which not only adds expense, but also makes the hardware bulky. Moreover, despite the redundant processing of data, it is still possible for such devices to inflate the air bag in the absence of a crash, which poses a serious safety hazard, especially if such erroneous inflation occurs at high vehicle speed. On the other hand, if the air bag fails to inflate in the event of a crash in which it should have been inflated, there is a substantial likelihood that the driver will be killed.
Such processing which affects the human life must be guaranteed fail-safe. However, according to the method of the prior art, though relatively high reliability has been maintained, fail-safety has not been guaranteed.